Polydimethylsiloxane (PDMS) is a synthetic polymer belonging to the silicone family, characterized by its unique combination of properties that have made it indispensable across countless industries. On product labels, this compound is most commonly listed as dimethicone, dimethylpolysiloxane, or the European food additive code E900. It is the most widely utilized silicon-based organic polymer in the world, valued for its stability and versatility.
Fundamental Composition and Properties
The core chemical identity of Polydimethylsiloxane is defined by its backbone, a chain of alternating silicon and oxygen atoms, known as a siloxane backbone. This structure is fundamentally different from that of common plastics, which are built on a carbon-based chain. Attached to the silicon atoms are two methyl groups (CH3), giving the compound its “dimethyl” designation. This silicon-oxygen framework allows the polymer chain to be exceptionally flexible, resulting in a very low glass transition temperature, allowing it to remain pliable and rubbery even at cold temperatures.
The presence of the methyl groups makes PDMS highly hydrophobic, meaning it repels water. This water-repellency, combined with a low surface tension, allows the substance to spread easily and form a thin, uniform film on surfaces. PDMS is also known for its unusual viscoelasticity, behaving as both a viscous liquid and an elastic solid. It is prized for its inertness, resisting chemical reactions, and its high thermal stability, allowing it to withstand a wide range of temperatures.
Widespread Consumer and Health Applications
In the realm of personal care, dimethicone is a common ingredient in shampoos and conditioners, serving as a conditioning agent to reduce friction and add shine to hair strands. It is also widely used in moisturizers, foundations, and primers because it forms a protective, non-greasy barrier on the skin that helps lock in moisture and smooth the appearance of fine lines.
In the food industry, Polydimethylsiloxane is utilized as an anti-foaming agent, designated as E900, to prevent liquids from frothing excessively during processing or cooking. This application is commonly found in frying oils and processed foods where excessive bubbling could impede manufacturing or lead to undesirable textures. PDMS is also incorporated into lubricants, sealants, and caulks due to its water-repellency and stability, offering durable protection and smooth operation in mechanical systems.
Polydimethylsiloxane’s inertness and biocompatibility make it a material of choice for medical and biomedical applications. It is used in the manufacturing of long-term medical implants, such as catheters and prosthetic devices, because it is non-reactive with human tissue. The polymer is also formulated into scar treatment sheets and gels, where its ability to form a flexible, breathable, and occlusive barrier aids in healing and scar reduction. PDMS is the standard material for fabricating microfluidic devices used in advanced biological research due to its optical clarity and gas permeability.
Safety Profile and Regulation
Regulatory bodies worldwide have established that Polydimethylsiloxane is safe for its intended uses, a conclusion based largely on its chemical inertness. The U.S. Food and Drug Administration (FDA) and other international agencies have classified the substance as non-toxic and biocompatible. When applied to the skin or consumed in food, the polymer’s large molecular structure prevents it from being absorbed into the body through the skin or the gastrointestinal tract. PDMS passes through the body without being metabolized or stored. While pure PDMS is not readily biodegradable, studies show it is effectively removed from wastewater during sewage treatment processes. Once in the environment, it can degrade when exposed to certain types of clay and moisture. The Cosmetic Ingredient Review Expert Panel has concluded that dimethicone and related polymers are safe when used in cosmetic formulations.